c++/1056: spurious warning on implicit conversion followed by promotion and comparison

[Wolfgang Bangerth]

The following reply was made to PR c++/1056; it has been noted by GNATS.

From: Wolfgang Bangerth <bangerth@ticam.utexas.edu>
To: gcc-bugs@gcc.gnu.org, <gcc-gnats@gcc.gnu.org>
Cc:  
Subject: Re: c++/1056: spurious warning on implicit conversion followed by
 promotion and comparison
Date: Sun, 10 Nov 2002 15:16:47 -0600 (CST)

 This report is about this code:
 ---------------------------------------
 struct X {
   operator unsigned short () const;
 };
 
 int main() {
   X s;
   unsigned long l;
 
   if (l == s);
   if (s == l);
 
   return 0;
 }
 ------------------------------
 and the following warnings:
 tmp/g> /home/bangerth/bin/gcc-3.3x-pre/bin/gcc -W -Wall -c x.cc
 x.cc: In function `int main()':
 x.cc:9: warning: comparison between signed and unsigned integer expressions
 x.cc:10: warning: comparison between signed and unsigned integer expressions
 
 I had initially thought that this may be due to argument promotion to a 
 signed type from the unsigned short the conversion operator returns, but 
 then the same should happen when we define "s" as an unsigned short right 
 from the start. However, this makes the warning go away. So I don't 
 know...
 
 W.
 
 -------------------------------------------------------------------------
 Wolfgang Bangerth              email:           bangerth@ticam.utexas.edu
                                www: http://www.ticam.utexas.edu/~bangerth